SIGNIFICANCE OF DOCOSAHEXAENOIC ACID FOR RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) LARVAE

N-3 fatty acids are essential for rainbow trout (Oncorhynchus mykiss). Our investigations specify the fatty acid requirements of rainbow tro ut larvae. One group of larvae was fed with Artemia ssp. rich in linol enic acid (18:3 n-3) and octadecatetraenoic acid (18:4 n-3), while the other group received a commercial fish feed containing high levels of long-chain polyunsaturated fatty acids (PUFA), mainly docosahexaenoic acid (22:6 n-3). After two and four weeks of feeding, the growth and fatty acid pattern of the larvae were determined. The fatty acid compo sition of the diet is reflected in the triglyceride composition of the fish, but there is no sign of conversion of 18:3 n-3 and 18:4 n-3 int o long-chain polyunsaturated fatty acids. This is caused by limited ch ain elongation rather than by low enzyme activity of desaturase. In th e triglycerides of the larvae, high levels of 18:4 n-3 were determined . This fatty acid was not transformed into the corresponding long-chai n polyunsaturated fatty acids. Deficiency of 22:6 n-3 resulted in redu ced larval growth. Therefore, it can be stated that docosahexaenoic ac id is essential for rainbow trout larvae.